Heat of combustion `DeltaH^(@)` for `C(s),H_(2)(g)` and `CH_(4)(g)` are `94, -68` and `-213Kcal//mol` . Then `DeltaH^(@)` for `C(s)+2H_(2)(g)rarrDeltaCH_(4)(g)` is

Options

A. `-17Kcal`
B. `111Kcal`
C. `-170Kcal`
D. `-85Kcal`

Answer

D

Explanation

For reaction,
`C(s)+2H_(2)(g)rarrCH_(4)(g),DeltaH^(@)=`?
`DeltaH^(@)=-[(Delta_(c)^(0)` of `CH_(2)-(Delta_(c)^(0)` of `C+2xxDeltaH_(c)^(0)` oof `H_(2))]`
`C+O_(2)rarrCO_(2),DeltaH=-94Kcal` (i)
`2H_(2)+O_(2)rarr2H_(2)O,DeltaH=-68xx2Kcal` (ii)
`CH_(4)+2O_(2)rarrCO_(2)+2H_(2)O,DeltaH=-213Kcal` (iii)
`"eq". (i)+(ii)-Eq(iii)`
`=-[(-213)-(-94+2xx-68)]Kcal//mol`
`=-[-213+230]=-17Kcal//mol`